Study On The Influence Of Model Resolution And Refined Upderlying Surface On Numerical Simulation Of "5·7" Rainstorm In Guangzhou Based On GSI Assimilation

The numerical simulation accuracy of the rainstorm in the warm sector of South China needs to be improved while it's a difficult point and hot spot.This study simulated and reappeared the local burst torrential rain in Guangzhou on 7 May 2017 well applying WRF v4.0 model using the GFS data with several sensitivity tests being performed.The impact of the horizontal and vertical resolution of model and refined underlying surface data on the mechanism of trigger and organization development of convective system in warm sector needs to be studied further.Firstly,the GSI assimilation system is used to assimilate multi-source observation data such as ground routine,sounding,and radar reflectivity to improve the background field of the model.Based on the assimilation scheme,the sensitivity tests were performed by varying vertical resolution in different levels of the troposphere,and the mesoscale numerical simulation primarily focused on the first stage of the “5·7” torrential rainstorm in Guangzhou.Then,1s(30 meters)high-resolution topographic and land cover data is introduced into the cloud-resolved numerical model which is based on the optimal mode horizontal and vertical resolution,and the land cover sensitivity test is set to simulate the “5·7” torrential rain in Guangzhou.The varying vertical resolution sensitivity tests result that the higher vertical resolution at the low levels test(LOW62)simulated stronger southerly returning flow,easterly wind,low-level wind convergence and temperature disturbances,which led to a stronger convective trigger.The higher vertical resolution at the middle levels experiments(MID68)was beneficial to a wide range of strong dry and cold air intrusion into the convection system.The released latent heat and instability energy may be the important reason for the development of convective system.The higher vertical resolution at the upper levels test(UPP71)not only described the upper divergence centers,which were related to outflow of upper level jet of the upper convective system,but also the other high divergence center around convective system were simulated well.The land cover sensitivity test with 1s high-resolution underlying surface data shows that high-resolution land cover data reduces the urban area in the model,and the green space and surface runoff increase.That causes the urban heat island effect in urban agglomerations to slow down and the ground sensible heat flux to decrease,resulting in the formation of a strong temperature gradient between Huadu district and Wangzi Mountain.The stronger high pressure recirculation and sea-land wind transport the warm and humid air to the inland,forming a warm and humid transport channel at the land and sea boundary.Then the constant warm and humid air in the front of the temperature gradient zone is strong forced uplift by hill resulting that convection triggers on local terrain and accelerate the organized processes.In this paper,the study on the influence of model resolution and refined underlying surface data on the numerical simulation provides an improved clue for the simulation of torrential rain in warm sector in southern China.At the same time,deepening the understanding of the influence of underlying surface data on urban heat islands and sea-land breeze circulation.The research has important indication significance for the forecast of heavy rain in the warm sector.